To ensure their guidance, guided urban public transport vehicles of this type have a guide assembly that permanently follows a continuous guide rail along the vehicle's entire route.
This guide assembly comprises V-shaped inclined rollers that roll on inclined tracks provided in the upper part of the head of the guide rail; this guide rail comprises a rail head with projecting flanks, under each of which a recess is located.
In order to ensure the safety of the vehicle and its passengers, it is essential that contact between the guide assembly, which is supported by the vehicle, and the guide rail—that is, between the guide rollers and the tracks on which they roll—be ensured at all times when the vehicle is moving.
To do this, the guide rollers are traditionally forced against the guide rail by an elastic return force, e.g., a spring arm.
While this type of system is adequate for normal guiding situations, exceptional situations exist wherein stress that is greater than the elastic stress may be exerted on the guide assembly in the opposite direction. This stress lifts the guide assembly above the guide rail and extracts it from the guide area. The guide rollers are pulled pull away from the guide rail, which possibly results in derailment.
This type of situation may occur, for example, when an object is located on the guide rail or inside the grooves running alongside the rail.
Indeed, because of exposure to bad weather and to the ambient environment of the guide track, it is common for the guide rail and/or its side grooves to be locally cluttered and/or obstructed with debris of all kinds—plants, ice, snow, rocks or other bodies or foreign objects left by accident or deliberately—that may constitute an obstacle for the guide rollers, causing them to be lifted up and off of the rail.
The lifting of the guide rollers and the extraction of the guide assembly out of the guide area of the rail represent unacceptable risks resulting in major problems, particularly the derailment of the guide assembly and subsequently of the vehicle.
To prevent the lifting and extraction of the guide assembly of these vehicles, according to the prior art, the guide rollers were equipped with flanges covering the outer face of the rollers and ending in a peripheral extension.
Traditionally, these flanges are part of or fixed to the guide rollers and turn with and at the same time as these rollers.
When the guide rollers are in operating position, each peripheral extension of the flanges fits into the lower recess of the guide rail, under the corresponding projecting flank of the rail head.
If the rollers experience lifting force, the peripheral extensions making up the flanges come up against the projecting flanks of the guide rail head and block the extraction of the guide assembly.